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This document describes the LLVM bitstream file format and the encoding of the LLVM IR into it.
What is commonly known as the LLVM bitcode file format (also, sometimes anachronistically known as bytecode) is actually two things: a bitstream container format and an encoding of LLVM IR into the container format.
The bitstream format is an abstract encoding of structured data, very similar to XML in some ways. Like XML, bitstream files contain tags, and nested structures, and you can parse the file without having to understand the tags. Unlike XML, the bitstream format is a binary encoding, and unlike XML it provides a mechanism for the file to self-describe “abbreviations”, which are effectively size optimizations for the content.
LLVM IR files may be optionally embedded into a wrapper structure, or in a native object file. Both of these mechanisms make it easy to embed extra data along with LLVM IR files.
This document first describes the LLVM bitstream format, describes the wrapper format, then describes the record structure used by LLVM IR files.
The bitstream format is literally a stream of bits, with a very simple structure. This structure consists of the following concepts:
Note that the llvm-bcanalyzer tool can be used to dump and inspect arbitrary bitstreams, which is very useful for understanding the encoding.
The first four bytes of a bitstream are used as an application-specific magic number. Generic bitcode tools may look at the first four bytes to determine whether the stream is a known stream type. However, these tools should notdetermine whether a bitstream is valid based on its magic number alone. New application-specific bitstream formats are being developed all the time; tools should not reject them just because they have a hitherto unseen magic number.
A bitstream literally consists of a stream of bits, which are read in order starting with the least significant bit of each byte. The stream is made up of a number of primitive values that encode a stream of unsigned integer values. These integers are encoded in two ways: either as Fixed Width Integers or as Variable Width Integers.
Fixed-width integer values have their low bits emitted directly to the file. For example, a 3-bit integer value encodes 1 as 001. Fixed width integers are used when there are a well-known number of options for a field. For example, boolean values are usually encoded with a 1-bit wide integer.
Variable-width integer (VBR) values encode values of arbitrary size, optimizing for the case where the values are small. Given a 4-bit VBR field, any 3-bit value (0 through 7) is encoded directly, with the high bit set to zero. Values larger than N-1 bits emit their bits in a series of N-1 bit chunks, where all but the last set the high bit.
For example, the value 27 (0x1B) is encoded as 1011 0011 when emitted as a vbr4 value. The first set of four bits indicates the value 3 (011) with a continuation piece (indicated by a high bit of 1). The next word indicates a value of 24 (011 << 3) with no continuation. The sum (3+24) yields the value 27.
6-bit characters encode common characters into a fixed 6-bit field. They represent the following characters with the following 6-bit values:
'a' .. 'z' --- 0 .. 25 'A' .. 'Z' --- 26 .. 51 '0' .. '9' --- 52 .. 61 '.' --- 62 '_' --- 63
This encoding is only suitable for encoding characters and strings that consist only of the above characters. It is completely incapable of encoding characters not in the set.
Occasionally, it is useful to emit zero bits until the bitstream is a multiple of 32 bits. This ensures that the bit position in the stream can be represented as a multiple of 32-bit words.
A bitstream is a sequential series of Blocks and Data Records. Both of these start with an abbreviation ID encoded as a fixed-bitwidth field. The width is specified by the current block, as described below. The value of the abbreviation ID specifies either a builtin ID (which have special meanings, defined below) or one of the abbreviation IDs defined for the current block by the stream itself.
The set of builtin abbrev IDs is:
Abbreviation IDs 4 and above are defined by the stream itself, and specify an abbreviated record encoding.
Blocks in a bitstream denote nested regions of the stream, and are identified by a content-specific id number (for example, LLVM IR uses an ID of 12 to represent function bodies). Block IDs 0-7 are reserved for standard blockswhose meaning is defined by Bitcode; block IDs 8 and greater are application specific. Nested blocks capture the hierarchical structure of the data encoded in it, and various properties are associated with blocks as the file is parsed. Block definitions allow the reader to efficiently skip blocks in constant time if the reader wants a summary of blocks, or if it wants to efficiently skip data it does not understand. The LLVM IR reader uses this mechanism to skip function bodies, lazily reading them on demand.
When reading and encoding the stream, several properties are maintained for the block. In particular, each block maintains:
BLOCKINFO
block is describing.As sub blocks are entered, these properties are saved and the new sub-block has its own set of abbreviations, and its own abbrev id width. When a sub-block is popped, the saved values are restored.
[ENTER_SUBBLOCK, blockidvbr8, newabbrevlenvbr4, <align32bits>, blocklen_32]
The ENTER_SUBBLOCK
abbreviation ID specifies the start of a new block record. The blockid
value is encoded as an 8-bit VBR identifier, and indicates the type of block being entered, which can be a standard block or an application-specific block. The newabbrevlen
value is a 4-bit VBR, which specifies the abbrev id width for the sub-block. The blocklen
value is a 32-bit aligned value that specifies the size of the subblock in 32-bit words. This value allows the reader to skip over the entire block in one jump.
[END_BLOCK, <align32bits>]
The END_BLOCK
abbreviation ID specifies the end of the current block record. Its end is aligned to 32-bits to ensure that the size of the block is an even multiple of 32-bits.
Data records consist of a record code and a number of (up to) 64-bit integer values. The interpretation of the code and values is application specific and may vary between different block types. Records can be encoded either using an unabbrev record, or with an abbreviation. In the LLVM IR format, for example, there is a record which encodes the target triple of a module. The code is MODULE_CODE_TRIPLE
, and the values of the record are the ASCII codes for the characters in the string.
[UNABBREV_RECORD, codevbr6, numopsvbr6, op0vbr6, op1vbr6, …]
An UNABBREV_RECORD
provides a default fallback encoding, which is both completely general and extremely inefficient. It can describe an arbitrary record by emitting the code and operands as VBRs.
For example, emitting an LLVM IR target triple as an unabbreviated record requires emitting the UNABBREV_RECORD
abbrevid, a vbr6 for the MODULE_CODE_TRIPLE
code, a vbr6 for the length of the string, which is equal to the number of operands, and a vbr6 for each character. Because there are no letters with values less than 32, each letter would need to be emitted as at least a two-part VBR, which means that each letter would require at least 12 bits. This is not an efficient encoding, but it is fully general.
[<abbrevid>, fields...]
An abbreviated record is a abbreviation id followed by a set of fields that are encoded according to the abbreviation definition. This allows records to be encoded significantly more densely than records encoded with theUNABBREV_RECORD type, and allows the abbreviation types to be specified in the stream itself, which allows the files to be completely self describing. The actual encoding of abbreviations is defined below.
The record code, which is the first field of an abbreviated record, may be encoded in the abbreviation definition (as a literal operand) or supplied in the abbreviated record (as a Fixed or VBR operand value).
Abbreviations are an important form of compression for bitstreams. The idea is to specify a dense encoding for a class of records once, then use that encoding to emit many records. It takes space to emit the encoding into the file, but the space is recouped (hopefully plus some) when the records that use it are emitted.
Abbreviations can be determined dynamically per client, per file. Because the abbreviations are stored in the bitstream itself, different streams of the same format can contain different sets of abbreviations according to the needs of the specific stream. As a concrete example, LLVM IR files usually emit an abbreviation for binary operators. If a specific LLVM module contained no or few binary operators, the abbreviation does not need to be emitted.
[DEFINE_ABBREV, numabbrevopsvbr5, abbrevop0, abbrevop1, …]
A DEFINE_ABBREV
record adds an abbreviation to the list of currently defined abbreviations in the scope of this block. This definition only exists inside this immediate block — it is not visible in subblocks or enclosing blocks. Abbreviations are implicitly assigned IDs sequentially starting from 4 (the first application-defined abbreviation ID). Any abbreviations defined in a BLOCKINFO
record for the particular block type receive IDs first, in order, followed by any abbreviations defined within the block itself. Abbreviated data records reference this ID to indicate what abbreviation they are invoking.
An abbreviation definition consists of the DEFINE_ABBREV
abbrevid followed by a VBR that specifies the number of abbrev operands, then the abbrev operands themselves. Abbreviation operands come in three forms. They all start with a single bit that indicates whether the abbrev operand is a literal operand (when the bit is 1) or an encoding operand (when the bit is 0).
The possible operand encodings are:
For example, target triples in LLVM modules are encoded as a record of the form [TRIPLE, 'a', 'b', 'c', 'd']
. Consider if the bitstream emitted the following abbrev entry:
[0, Fixed, 4] [0, Array] [0, Char6]
When emitting a record with this abbreviation, the above entry would be emitted as:
[4abbrevwidth, 24, 4vbr6, 06, 16, 26, 36]
These values are:
TRIPLE
records within LLVM IR file MODULE_BLOCK
blocks."abcd"
.With this abbreviation, the triple is emitted with only 37 bits (assuming a abbrev id width of 3). Without the abbreviation, significantly more space would be required to emit the target triple. Also, because the TRIPLE
value is not emitted as a literal in the abbreviation, the abbreviation can also be used for any other string value.
In addition to the basic block structure and record encodings, the bitstream also defines specific built-in block types. These block types specify how the stream is to be decoded or other metadata. In the future, new standard blocks may be added. Block IDs 0-7 are reserved for standard blocks.
The BLOCKINFO
block allows the description of metadata for other blocks. The currently specified records are:
[SETBID (#1), blockid] [DEFINE_ABBREV, ...] [BLOCKNAME, ...name...] [SETRECORDNAME, RecordID, ...name...]
The SETBID
record (code 1) indicates which block ID is being described. SETBID
records can occur multiple times throughout the block to change which block ID is being described. There must be a SETBID
record prior to any other records.
Standard DEFINE_ABBREV
records can occur inside BLOCKINFO
blocks, but unlike their occurrence in normal blocks, the abbreviation is defined for blocks matching the block ID we are describing, not the BLOCKINFO
block itself. The abbreviations defined in BLOCKINFO
blocks receive abbreviation IDs as described in DEFINE_ABBREV.
The BLOCKNAME
record (code 2) can optionally occur in this block. The elements of the record are the bytes of the string name of the block. llvm-bcanalyzer can use this to dump out bitcode files symbolically.
The SETRECORDNAME
record (code 3) can also optionally occur in this block. The first operand value is a record ID number, and the rest of the elements of the record are the bytes for the string name of the record. llvm-bcanalyzer can use this to dump out bitcode files symbolically.
Note that although the data in BLOCKINFO
blocks is described as “metadata,” the abbreviations they contain are essential for parsing records from the corresponding blocks. It is not safe to skip them.
Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper structure. This structure contains a simple header that indicates the offset and size of the embedded BC file. This allows additional information to be stored alongside the BC file. The structure of this file header is:
[Magic32, Version32, Offset32, Size32, CPUType32]
Each of the fields are 32-bit fields stored in little endian form (as with the rest of the bitcode file fields). The Magic number is always 0x0B17C0DE
and the version is currently always 0
. The Offset field is the offset in bytes to the start of the bitcode stream in the file, and the Size field is the size in bytes of the stream. CPUType is a target-specific value that can be used to encode the CPU of the target.
Bitcode files for LLVM IR may also be wrapped in a native object file (i.e. ELF, COFF, Mach-O). The bitcode must be stored in a section of the object file named __LLVM,__bitcode
for MachO and .llvmbc
for the other object formats. This wrapper format is useful for accommodating LTO in compilation pipelines where intermediate objects must be native object files which contain metadata in other sections.
Not all tools support this format.
LLVM IR is encoded into a bitstream by defining blocks and records. It uses blocks for things like constant pools, functions, symbol tables, etc. It uses records for things like instructions, global variable descriptors, type descriptions, etc. This document does not describe the set of abbreviations that the writer uses, as these are fully self-described in the file, and the reader is not allowed to build in any knowledge of this.
The magic number for LLVM IR files is:
[‘B’8, ‘C’8, 0x04, 0xC4, 0xE4, 0xD4]
Variable Width Integer encoding is an efficient way to encode arbitrary sized unsigned values, but is an extremely inefficient for encoding signed values, as signed values are otherwise treated as maximally large unsigned values.
As such, signed VBR values of a specific width are emitted as follows:
With this encoding, small positive and small negative values can both be emitted efficiently. Signed VBR encoding is used in CST_CODE_INTEGER
and CST_CODE_WIDE_INTEGER
records within CONSTANTS_BLOCK
blocks. It is also used for phi instruction operands in MODULE_CODE_VERSION 1.
LLVM IR is defined with the following blocks:
The MODULE_BLOCK
block (id 8) is the top-level block for LLVM bitcode files, and each bitcode file must contain exactly one. In addition to records (described below) containing information about the module, a MODULE_BLOCK
block may contain the following sub-blocks:
[VERSION, version#]
The VERSION
record (code 1) contains a single value indicating the format version. Versions 0, 1 and 2 are supported at this time. The difference between version 0 and 1 is in the encoding of instruction operands in each FUNCTION_BLOCK.
In version 0, each value defined by an instruction is assigned an ID unique to the function. Function-level value IDs are assigned starting from NumModuleValues
since they share the same namespace as module-level values. The value enumerator resets after each function. When a value is an operand of an instruction, the value ID is used to represent the operand. For large functions or large modules, these operand values can be large.
The encoding in version 1 attempts to avoid large operand values in common cases. Instead of using the value ID directly, operands are encoded as relative to the current instruction. Thus, if an operand is the value defined by the previous instruction, the operand will be encoded as 1.
For example, instead of
#n = load #n-1 #n+1 = icmp eq #n, #const0 br #n+1, label #(bb1), label #(bb2)
version 1 will encode the instructions as
#n = load #1 #n+1 = icmp eq #1, (#n+1)-#const0 br #1, label #(bb1), label #(bb2)
Note in the example that operands which are constants also use the relative encoding, while operands like basic block labels do not use the relative encoding.
Forward references will result in a negative value. This can be inefficient, as operands are normally encoded as unsigned VBRs. However, forward references are rare, except in the case of phi instructions. For phi instructions, operands are encoded as Signed VBRs to deal with forward references.
In version 2, the meaning of module records FUNCTION
, GLOBALVAR
, ALIAS
, IFUNC
and COMDAT
change such that the first two operands specify an offset and size of a string in a string table (see STRTAB_BLOCK Contents), the function name is removed from the FNENTRY
record in the value symbol table, and the top-level VALUE_SYMTAB_BLOCK
may only containFNENTRY
records.
[TRIPLE, ...string...]
The TRIPLE
record (code 2) contains a variable number of values representing the bytes of the target triple
specification string.
[DATALAYOUT, ...string...]
The DATALAYOUT
record (code 3) contains a variable number of values representing the bytes of the target datalayout
specification string.
[ASM, ...string...]
The ASM
record (code 4) contains a variable number of values representing the bytes of module asm
strings, with individual assembly blocks separated by newline (ASCII 10) characters.
MODULE_CODE_SECTIONNAME Record
[SECTIONNAME, ...string...]
The SECTIONNAME
record (code 5) contains a variable number of values representing the bytes of a single section name string. There should be one SECTIONNAME
record for each section name referenced (e.g., in global variable or function section
attributes) within the module. These records can be referenced by the 1-based index in the section fields of GLOBALVAR
or FUNCTION
records.
[DEPLIB, ...string...]
The DEPLIB
record (code 6) contains a variable number of values representing the bytes of a single dependent library name string, one of the libraries mentioned in a deplibs
declaration. There should be one DEPLIB
record for each library name referenced.
[GLOBALVAR, strtab offset, strtab size, pointer type, isconst, initid, linkage, alignment, section,visibility, threadlocal, unnamed_addr, externally_initialized, dllstorageclass, comdat, attributes,preemptionspecifier]
The GLOBALVAR
record (code 7) marks the declaration or definition of a global variable. The operand fields are:
external
: code 0weak
: code 1appending
: code 2internal
: code 3linkonce
: code 4dllimport
: code 5dllexport
: code 6extern_weak
: code 7common
: code 8private
: code 9weak_odr
: code 10linkonce_odr
: code 11available_externally
: code 12default
: code 0hidden
: code 1protected
: code 2not thread local
: code 0thread local; default TLS model
: code 1localdynamic
: code 2initialexec
: code 3localexec
: code 4unnamed_addr
attribute of this variable:
unnamed_addr
: code 0unnamed_addr
: code 1local_unnamed_addr
: code 2default
: code 0dllimport
: code 1dllexport
: code 2dso_preemptable
: code 0dso_local
: code 1[FUNCTION, strtab offset, strtab size, type, callingconv, isproto, linkage, paramattr, alignment, section,visibility, gc, prologuedata, dllstorageclass, comdat, prefixdata, personalityfn, preemptionspecifier]
The FUNCTION
record (code 8) marks the declaration or definition of a function. The operand fields are:
ccc
: code 0 * fastcc
: code 8 * coldcc
: code 9 * webkit_jscc
: code 12 * anyregcc
: code 13 * preserve_mostcc
: code 14 * preserve_allcc
: code 15 * swiftcc
: code 16 * cxx_fast_tlscc
: code 17 * x86_stdcallcc
: code 64 * x86_fastcallcc
: code 65 * arm_apcscc
: code 66 * arm_aapcscc
: code 67 * arm_aapcs_vfpcc
: code 68[ALIAS, strtab offset, strtab size, alias type, aliasee val#, linkage, visibility, dllstorageclass,threadlocal, unnamed_addr, preemptionspecifier]
The ALIAS
record (code 9) marks the definition of an alias. The operand fields are
[GCNAME, ...string...]
The GCNAME
record (code 11) contains a variable number of values representing the bytes of a single garbage collector name string. There should be one GCNAME
record for each garbage collector name referenced in function gc
attributes within the module. These records can be referenced by 1-based index in the gc fields of FUNCTION
records.
The PARAMATTR_BLOCK
block (id 9) contains a table of entries describing the attributes of function parameters. These entries are referenced by 1-based index in the paramattr field of module block FUNCTION records, or within the attrfield of function block INST_INVOKE
and INST_CALL
records.
Entries within PARAMATTR_BLOCK
are constructed to ensure that each is unique (i.e., no two indices represent equivalent attribute lists).
[ENTRY, attrgrp0, attrgrp1, ...]
The ENTRY
record (code 2) contains a variable number of values describing a unique set of function parameter attributes. Each attrgrp value is used as a key with which to look up an entry in the attribute group table described in the PARAMATTR_GROUP_BLOCK
block.
PARAMATTR_CODE_ENTRY_OLD Record
Note
This is a legacy encoding for attributes, produced by LLVM versions 3.2 and earlier. It is guaranteed to be understood by the current LLVM version, as specified in the IR Backwards Compatibility policy.
[ENTRY, paramidx0, attr0, paramidx1, attr1...]
The ENTRY
record (code 1) contains an even number of values describing a unique set of function parameter attributes. Each paramidx value indicates which set of attributes is represented, with 0 representing the return value attributes, 0xFFFFFFFF representing function attributes, and other values representing 1-based function parameters. Each attr value is a bitmap with the following interpretation:
zeroext
signext
noreturn
inreg
sret
nounwind
noalias
byval
nest
readnone
readonly
noinline
alwaysinline
optsize
ssp
sspreq
align n
nocapture
noredzone
noimplicitfloat
naked
inlinehint
alignstack n
, represented as the logarithm base 2 of the requested alignment, plus 1The PARAMATTR_GROUP_BLOCK
block (id 10) contains a table of entries describing the attribute groups present in the module. These entries can be referenced within PARAMATTR_CODE_ENTRY
entries.
PARAMATTR_GRP_CODE_ENTRY Record
[ENTRY, grpid, paramidx, attr0, attr1, ...]
The ENTRY
record (code 3) contains grpid and paramidx values, followed by a variable number of values describing a unique group of attributes. The grpid value is a unique key for the attribute group, which can be referenced within PARAMATTR_CODE_ENTRY
entries. The paramidx value indicates which set of attributes is represented, with 0 representing the return value attributes, 0xFFFFFFFF representing function attributes, and other values representing 1-based function parameters.
Each attr is itself represented as a variable number of values:
kind, key [, ...], [value [, ...]]
Each attribute is either a well-known LLVM attribute (possibly with an integer value associated with it), or an arbitrary string (possibly with an arbitrary string value associated with it). The kind value is an integer code distinguishing between these possibilities:
For well-known attributes (code 0 or 1), the key value is an integer code identifying the attribute. For attributes with an integer argument (code 1), the value value indicates the argument.
For string attributes (code 3 or 4), the key value is actually a variable number of values representing the bytes of a null-terminated string. For attributes with a string argument (code 4), the value value is similarly a variable number of values representing the bytes of a null-terminated string.
The integer codes are mapped to well-known attributes as follows.
align(<n>)
alwaysinline
byval
inlinehint
inreg
minsize
naked
nest
noalias
nobuiltin
nocapture
noduplicates
noimplicitfloat
noinline
nonlazybind
noredzone
noreturn
nounwind
optsize
readnone
readonly
returned
returns_twice
signext
alignstack(<n>)
ssp
sspreq
sspstrong
sret
sanitize_address
sanitize_thread
sanitize_memory
uwtable
zeroext
builtin
cold
optnone
inalloca
nonnull
jumptable
dereferenceable(<n>)
dereferenceable_or_null(<n>)
convergent
safestack
argmemonly
swiftself
swifterror
norecurse
inaccessiblememonly
inaccessiblememonly_or_argmemonly
allocsize(<EltSizeParam>[, <NumEltsParam>])
writeonly
speculatable
strictfp
sanitize_hwaddress
nocf_check
optforfuzzing
shadowcallstack
Note
The allocsize
attribute has a special encoding for its arguments. Its two arguments, which are 32-bit integers, are packed into one 64-bit integer value (i.e. (EltSizeParam << 32) | NumEltsParam
), with NumEltsParam
taking on the sentinel value -1 if it is not specified.
The TYPE_BLOCK
block (id 17) contains records which constitute a table of type operator entries used to represent types referenced within an LLVM module. Each record (with the exception of NUMENTRY) generates a single type table entry, which may be referenced by 0-based index from instructions, constants, metadata, type symbol table entries, or other type operator records.
Entries within TYPE_BLOCK
are constructed to ensure that each entry is unique (i.e., no two indices represent structurally equivalent types).
[NUMENTRY, numentries]
The NUMENTRY
record (code 1) contains a single value which indicates the total number of type code entries in the type table of the module. If present, NUMENTRY
should be the first record in the block.
[VOID]
The VOID
record (code 2) adds a void
type to the type table.
[HALF]
The HALF
record (code 10) adds a half
(16-bit floating point) type to the type table.
[FLOAT]
The FLOAT
record (code 3) adds a float
(32-bit floating point) type to the type table.
[DOUBLE]
The DOUBLE
record (code 4) adds a double
(64-bit floating point) type to the type table.
[LABEL]
The LABEL
record (code 5) adds a label
type to the type table.
[OPAQUE]
The OPAQUE
record (code 6) adds an opaque
type to the type table, with a name defined by a previously encountered STRUCT_NAME
record. Note that distinct opaque
types are not unified.
[INTEGER, width]
The INTEGER
record (code 7) adds an integer type to the type table. The single width field indicates the width of the integer type.
[POINTER, pointee type, address space]
The POINTER
record (code 8) adds a pointer type to the type table. The operand fields are
Note
This is a legacy encoding for functions, produced by LLVM versions 3.0 and earlier. It is guaranteed to be understood by the current LLVM version, as specified in the IR Backwards Compatibility policy.
[FUNCTION_OLD, vararg, ignored, retty, ...paramty... ]
The FUNCTION_OLD
record (code 9) adds a function type to the type table. The operand fields are
[ARRAY, numelts, eltty]
The ARRAY
record (code 11) adds an array type to the type table. The operand fields are
[VECTOR, numelts, eltty]
The VECTOR
record (code 12) adds a vector type to the type table. The operand fields are
[X86_FP80]
The X86_FP80
record (code 13) adds an x86_fp80
(80-bit floating point) type to the type table.
[FP128]
The FP128
record (code 14) adds an fp128
(128-bit floating point) type to the type table.
[PPC_FP128]
The PPC_FP128
record (code 15) adds a ppc_fp128
(128-bit floating point) type to the type table.
[METADATA]
The METADATA
record (code 16) adds a metadata
type to the type table.
[X86_MMX]
The X86_MMX
record (code 17) adds an x86_mmx
type to the type table.
[STRUCT_ANON, ispacked, ...eltty...]
The STRUCT_ANON
record (code 18) adds a literal struct type to the type table. The operand fields are
[STRUCT_NAME, ...string...]
The STRUCT_NAME
record (code 19) contains a variable number of values representing the bytes of a struct name. The next OPAQUE
or STRUCT_NAMED
record will use this name.
[STRUCT_NAMED, ispacked, ...eltty...]
The STRUCT_NAMED
record (code 20) adds an identified struct type to the type table, with a name defined by a previously encountered STRUCT_NAME
record. The operand fields are
[FUNCTION, vararg, retty, ...paramty... ]
The FUNCTION
record (code 21) adds a function type to the type table. The operand fields are
The CONSTANTS_BLOCK
block (id 11) …
The FUNCTION_BLOCK
block (id 12) …
In addition to the record types described below, a FUNCTION_BLOCK
block may contain the following sub-blocks:
The VALUE_SYMTAB_BLOCK
block (id 14) …
The METADATA_BLOCK
block (id 15) …
The METADATA_ATTACHMENT
block (id 16) …
The STRTAB
block (id 23) contains a single record (STRTAB_BLOB
, id 1) with a single blob operand containing the bitcode file’s string table.
Strings in the string table are not null terminated. A record’s strtab offset and strtab size operands specify the byte offset and size of a string within the string table.
The string table is used by all preceding blocks in the bitcode file that are not succeeded by another intervening STRTAB
block. Normally a bitcode file will have a single string table, but it may have more than one if it was created by binary concatenation of multiple bitcode files.
文章浏览阅读8.5k次,点赞6次,收藏5次。有用的话记得回过头请给本文点个赞,感谢您的支持!LinAlgError: SVD did not converge in Linear Least Squares说明在拟合时,y值里存在nan值,ps:虽然你的原始文件中可能没有nan值,但是可能存在数值类型不是float型或完全的整型的数据,导致读出来的数据中有nan值,我就遇到一个,如图,读出来有一个是nan值,原始文件中是一个float型数字。解决方法,去掉该数据。y = lsit(y)nan_index = []for i in r_svd did not converge in linear least squares
文章浏览阅读127次。今天,看了同学写的HTML代码很糟糕.就自己重写了一下.了解了一些HTML.CSS知识.现记录在这里.先给大家一个比较好的CSS教程网站:http://www.w3school.com.cn/css/index.aspCSS 概述CSS 指层叠样式表 (Cascading Style Sheets)样式定义如何显示 HTML 元素样式通常存储在样式表中把样式添加..._cgi 生成含有css的html文件
文章浏览阅读2k次,点赞3次,收藏11次。- MIB通过BCH传输信道和PBCH物理信道传输;- QPSK调制;- 它包含了解码 *SystemInformationBlockType1 (SIB1)* 所需的必要参数;- 它的传输周期为80毫秒,在这80毫秒内进行重复传输;- 它在OFDM 的符号1、2、3上传输;- 根据TS 38.211,它在符号1和3上使用0~239的子载波号,而在符号2上,使用0\~47的子载波号和192\~239的子载波号;_mib rlc
文章浏览阅读3.8w次。今天在对原来的项目进行运行时,突然程序报出java.sql.SQLException: Listener refused the connection with the following error:ORA-12519, TNS:no appropriate service handler found 这个错误,之前一直运行都是好好的,于是乎,就各种查找相关的解决方法,网上查找到的原_oracle.net.ns.netexception: listener refused the connection with the followi
文章浏览阅读5.1k次,点赞8次,收藏43次。继ros里面A*全局规划之后,再解析局部路径算法dwa的整个算法调用过程,至于细节放到后面的章节去写 dwa的整体思路网上有很多相关的资料了https://blog.csdn.net/heyijia0327/article/details/44983551具体的可以参看这一篇博客 本篇文章的话只要是说navigation包里面的调用过程,不关心整体思路前期将局部路径..._ros dwa算法源码解析
文章浏览阅读309次。很多人在白塞氏病的阴影下,迟迟的难以走出,原因就是得不到良好的治疗。这部分患者中有一些是年轻的夫妇,这给打算要孩子的他们无疑带来了很大的困扰。自己本已饱受白塞氏病之苦,如果此时打算要孩子会不会遗传给孩子,让孩子继续这痛苦和折磨?本章就由专家为大家讲解。首先,专家介绍说白塞氏病是一种自身免疫性疾病,临床上以口腔溃疡、生殖器溃疡、眼炎及皮肤损害为突出表现,但是并不会对患者的生殖系统内部产生影响,造成...
文章浏览阅读1k次。1.打开 VS 创建一个 安装项目,如下图:创建成功后,如下图: 2.安装项目的 文件夹介绍及其使用A.应用程序文件夹 : 主要功能,存储需要打包,执行程序,以及资源文件。B.用户的“程序”菜单 :主要功能,左下角windows 快捷方式 存放的地方 C.用户桌面 : 主要功能,用户机器 桌面的快捷方式 存放的地方 3.操作步骤1.配置应用程序文件夹 2.配置应用程序菜单A.添加文件的方法_vs winform 项目打包 怎么把python打进去
文章浏览阅读2.4k次,点赞2次,收藏30次。FPGA面试真题解析1、1、 十进制46.25对应的二进制表达式为( )。(硬件逻辑实习岗)A 101110.11 B 101101.01 C 101110.1 D 101110.01解析:这个问题看上去很简单,那是因为我们平时可以打开电脑上的计算器,然后用程序员功能立刻就能出结果,但是笔试的时候我们并不能使用这种“作弊“的功能,所以还是要会手算。可能很多同学数电是大一大二时学习的,很久没有接触过这么基础的问题了,那就让我们一起来回忆下吧。首先这个题_fpga二进制编码为啥用较多组合逻辑
文章浏览阅读1k次。SELECT语句 SELECT [ ALL | DISTINCT { * | expression | column1_name [ , column2_name ] [ , … ] }FROM { table1_name | ( subquery ) } [ alias ][ , { table2_name | ( subquery ) } [ alias ] , … ][ _oracle删除语句带子查询 原理
文章浏览阅读7k次,点赞4次,收藏16次。插入——端子——点击端子。选择端子,没别插入到图纸中;勾选多层端子,输入端子层数量;将X5和X6连个端子合并为一个端子排;不同行/列,生成多个端子排;选中端子,可以拖放插入,也可以单个放置;默认端子如果不是想插入的端子,按退格键选择;设备——端子——导航器。或者使用3连接点的端子和4连接点的端子组合;通常选择带鞍型跳线的端子,2个连接点;双击X6——将完整设备标识符修改为X5:2;X5端子排的第二个;已使用端子和未使用端子,端子前的购物车符号不同;如果放置在同一列/行,自动生成为同一个端子排;_eplan端子排
文章浏览阅读683次,点赞6次,收藏18次。Vue是一套构建用户界面的渐进式框架。它与其他大型框架(如React和Angular)一样,都是用于构建用户界面的JavaScript框架。Vue被设计自底向上逐层应用,其核心库只关注视图层,不仅易于上手,也便于与第三方库或已有项目整合。vue还是单⻚面应用程序总而言之vue便是用于构建用户界面的渐进式框架,采用自底向上增量开发的设计。(重点)
文章浏览阅读1.1w次,点赞77次,收藏549次。多线程经典面试题59问。1.什么是活锁、饥饿、无锁、死锁?死锁、活锁、饥饿是关于多线程是否活跃出现的运行阻塞障碍问题,如果线程出现 了这三种情况,即线程不再活跃,不能再正常地执行下去了。死锁死锁是多线程中最差的一种情况,多个线程相互占用对方的资源的锁,而又相互等 对方释放锁,此时若无外力干预,这些线程则一直处理阻塞的假死状态,形成死锁。 举个例子,A 同学抢了 B 同学的钢笔,B 同学..._多线程锁面试题